Definition and Classification
Aggregates are granular mineral materials used as primary constituents in concrete, asphalt, and other composite building materials. They comprise approximately 60–75% of concrete by volume and 90–95% of asphalt mixtures by mass. Standard classifications distinguish between coarse aggregates (particles >4.75 mm) and fine aggregates (particles <4.75 mm), with further subdivision into natural and manufactured types.
Material Types and Sources
Natural aggregates include crushed stone, gravel, and sand extracted from quarries, riverbeds, and coastal deposits. Manufactured aggregates are produced by crushing rock, recycled concrete, or industrial byproducts. Common material sources encompass granite, limestone, basalt, and dolomite. Recycled concrete aggregates (RCA) have gained significance in circular economy applications, though they typically exhibit higher water absorption (2–8%) compared to virgin stone (0.5–2%).
Key Physical Properties
Bulk density typically ranges from 1,400–1,700 kg/m³ for natural stone aggregates. Particle size distribution is defined by sieve analysis according to EN 933-1; maximum nominal size commonly ranges from 4 mm to 32 mm depending on application. Flakiness index, measured per EN 933-3, should not exceed 35–40% for quality assurance. Water absorption capacity varies between 0.1% and 3.0% by mass for natural materials. Los Angeles abrasion value (EN 1097-2) indicates mechanical durability; acceptable limits range from 15–35 depending on exposure class and application.
Production and Processing
Primary crushing reduces raw stone to target sizes, followed by secondary and tertiary crushing for finer gradations. Washing removes dust and clay contaminants, improving bond characteristics with binders. Screening and classification employ vibrating sieves or spiral classifiers to achieve specified particle size curves. Production capacity for modern aggregate plants reaches 300–500 tonnes per hour for coarse material and 100–250 tonnes per hour for fine fractions.
Quality Standards and Testing
EN 12620 (Aggregates for Concrete) and EN 13043 (Aggregates for Bituminous Mixtures) establish material requirements across Europe. Testing protocols include granulometric analysis (EN 933-1), density determination (EN 1097-6), and soundness evaluation via magnesium sulfate immersion (EN 1367-2). Compressive strength of aggregate particles (EN 1097-1) must meet minimum values of 90–110 MPa for demanding applications.
Storage and Handling
Aggregates are stored in open stockpiles or enclosed bunkers, with separation by grade to prevent commingling. Stockpile volumes for typical projects range from 50–500 m³. Moisture content fluctuates seasonally (3–8% for sand, 1–4% for stone), affecting batching accuracy in production. Conveyor systems, bucket elevators, and front-end loaders are standard handling equipment; transfer heights may reach 15–25 meters in integrated processing facilities.
Regulatory and Environmental Considerations
Extraction operations require permits under national mining and environmental legislation. Water management and dust control are mandatory; residual fines content should not exceed 2–5% for high-performance applications. Sustainable sourcing increasingly emphasizes recycled aggregates and industrial waste utilization (slag, fly ash) to reduce virgin material extraction and transportation emissions.
